Cerebral protection during carotid endarterectomy and downstream vascular protection during other surgeries

ABSTRACT

A shunt and method of use for maintaining distal blood flow during an arteriotomy procedure is disclosed. The shunt includes a first tubular member having a proximal end, a distal end, and a lumen therebetween. The proximal end has an opening in communication with the lumen, and the proximal opening is adapted to receive blood from a first region of an artery. The distal end has an opening in communication with the lumen, and the distal opening is adapted to release blood into a second region of the artery. The shunt includes a second tubular member having a proximal end, a distal end, and a lumen therebetween which either merges and communicates at its distal end with the lumen of the first tubular member, or rides separate and parallel to it. The shunt also includes a hemostatic valve attached to the proximal end of the second tubular member, the valve acting to prevent loss of blood from the lumen of the second tubular member and to permit the introduction of a medical device into the lumen of the second tubular member and into the artery. In use, the distal opening of the shunt is inserted into the second region of an artery and secured to the lumen of the artery. A blood filter device is deployed within the artery. The proximal opening of the shunt is inserted into the first region of the artery and secured to the lumen of the artery. Endarterectomy is performed on the region of the artery which lies between the proximal opening and the distal opening of the shunt, and embolic material dislodged during the procedure is captured by the filter.

FIELD OF THE INVENTION

This invention relates to carotid endarterectomy surgery. Moreparticularly, it relates to methods and apparatus for improvingendarterectomy procedures by using blood filtration to protect thepatient from embolization during these vascular surgeries.

BACKGROUND OF THE INVENTION

Endarterectomy is a surgical procedure which generally includes theremoval of the lining of an artery. Typically the artery is dissectedlongitudinally to expose an affected region from which plaque and othermaterials may be removed. Endarterectomy can be performed on almost anymajor artery that is diseased or blocked, and is most commonly used forthe carotid, femoral, and popliteal arteries.

In a typical procedure, the surgeon makes a standard vertical incisionin the neck of a patient, or a transverse incision corresponding to askin line of the neck. The incision is deepened through and aroundsubcutaneous adipose tissue, platysma muscle, the branches of theexternal jugular vein, and the border of the sternocleidomastoid musclein order to expose the carotid sheath. Careful dissection is used toexpose the common carotid artery and its external and internal branches.Vascular clamps are applied to the internal carotid artery, externalcarotid artery, and common carotid artery, and a vertical arteriotomy ismade in the common carotid artery, typically below the bifurcation. Theincision may be advanced into the internal carotid artery to a pointbeyond the area which contains plaque material.

An indwelling shunt may then be installed in order to bypass the clampedregion of the artery so that brain perfusion is not disrupted. Theartery is then clamped proximal and distal about the shunt in order toisolate a bloodless region for endarterectomy. Atheromatous material isthen removed, first from the common carotid artery, then from theexternal carotid artery, and generally last from the internal carotidartery. After the endarterectomy procedure has been performed, thesurgeon cleans the region of plaque fragments before removal of theshunt and closure of the vascular incision.

The above-described procedure, however, suffers from a deficiency whichrelates to the escape of embolic material which may lead to devastatingneurologic complications, particularly when emboli escape through theinternal carotid artery. Emboli may be produced through any step of theprocedure where mechanical forces are applied to the artery, and thesemanipulations include clamping, unclamping, applying a tourniquet,dissecting the vessel, inserting and removing a bypass shunt, removingatheromatous material, cleaning the affected site, and suturing thevessel. Therefore, a need exists for an improved endarterectomyprocedure and apparatus which will enable the surgeon to minimize theproduction of embolic material and to prevent the escape of embolicmaterial during carotid endarterectomy, arteriotomy, and other vascularsurgeries.

SUMMARY OF THE INVENTION

A dramatic improvement in the neurologic outcome of patients undergoingcarotid endarterectomy, and arteriotomy procedures generally, can beachieved by using a blood filter device to capture and remove dislodgedembolic material during the surgical procedure in accordance with ourinvention. Thus, the invention provides novel methods and apparatus forprotecting a patient from embolization during arteriotomy procedures. Inone embodiment, the invention provides a bypass tubing or indwellingshunt, having a main lumen for blood bypass and a second, branchinglumen adapted to receive an elongated blood filtration instrument, orother surgical device (e.g., an angioplasty catheter, stent catheter,atherectomy catheter) and to allow passage of same into an artery distalto the endarterectomy region. The branching secondary lumen can eithermerge and communicate with the main lumen of the shunt, or may extend toa distal opening separate from the blood bypass lumen of the device.

In another embodiment, a standard single-lumen indwelling shunt is usedin accordance with the disclosure of Loftus, Carotid EndarterectomyPrinciples and Techniques; Quality Medical Publishing, Inc.: St. Louis,Mo., 1995 (this and all other references cited herein are expresslyincorporated by reference as if fully set forth in their entiretyherein), and an introducer sheath and filtration catheter are providedfor deployment distal to the site of standard carotid endarterectomy.The introducer sheath includes a hemostatic valve adapted to receive afiltration catheter. The filtration catheter typically includes acatheter sheath, an elongated control member, a control mechanism at aproximal end of the control member, and a filtration assembly whichincludes an expansion frame and filter mesh at a distal region of thecontrol member, the expansion frame being operable to enlarge from acontracted condition to an expanded condition which covers all of, or asubstantial portion of the cross-sectional area of a vessel. Inalternative embodiments, a filter is disposed on a guidewire or tubingfor use in carotid artery bypass to capture clots and atheroscleroticmaterial released during endarterectomy.

According to the methods of the present invention, an affected region ofan artery is isolated, clamped, and dissected as disclosed in Loftus,Carotid Endarterectomy Principles and Techniques; Quality MedicalPublishing, Inc.: St. Louis, Mo., 1995, and Smith, The SurgicalTreatment of Peripheral Vascular Disease, Chapter 142, in "The Heart,Arteries, and Veins," Vol. 2, Ed. J. Willis Hurst; McGraw-HillInformation Services Corp., 1990. An indwelling shunt as describedherein is then inserted so that the distal region penetrates into thedistal artery and is secured by a distal artery clamp, while theproximal region penetrates into the proximal artery and is secured by aclamp proximal to the region of arteriotomy. A blood filter device isdeployed through the second lumen of the indwelling shunt as disclosedherein, is advanced within the blood vessel, and then expanded to covera substantial cross-sectional area of the artery distal to thearteriotomy region. Endarterectomy is performed in accordance withstandard procedures to remove atherosclerotic material from the affectedregion of the artery.

According to an alternative method, a non-indwelling shunt or plastictubing as disclosed herein is used to bypass an affected region of theartery. After the carotid artery is exposed, an incision is madeproximal to the site where the common carotid artery cross-clamp will beplaced. Plastic tubing having an appropriate size is placed in thisincision and then extended distally, past the site where the internalcarotid artery cross-clamp will be placed, and distal to theatherosclerotic plaque, where the plastic tubing reenters the carotidartery through a second incision. A filter device is deployed in theinternal carotid artery through a side-port on the shunt, or the filtermay be deployed by an expansion mechanism intrinsic to the tubingitself. The common and internal carotid arteries are then clamped. Thecarotid artery is incised, plaque removed, the operative site rinsedwith sterile saline or water, and the carotid artery, with or without agraft, is closed. The proximal and distal cross-clamps are removed, andcirculation through the repaired carotid artery is restored as discussedherein. The proximal end of the plastic tubing is removed from thecommon carotid artery and the proximal incision is closed. The filter,including captured embolic material, is retracted after several minutes,typically at least 5 minutes, more preferably at least 10 minutes, andthe distal end of the shunt is removed. Finally, the distal incision isclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a common or merging lumen shunt in accordance with oneembodiment of the present invention;

FIG. 2 depicts a non-communicating lumen shunt in accordance withanother aspect of the present invention;

FIG. 3 depicts an indwelling common lumen shunt and filter deployedwithin an artery during an endarterectomy procedure;

FIG. 3A is a cross-sectional view taken through section line 3A--3A ofthe shunt and vessel depicted in FIG. 3;

FIG. 4 depicts a standard indwelling shunt during endarterectomy and afiltration catheter deployed through an introducer sheath;

FIG. 5 depicts a non-indwelling shunt bypassing a region of the commonand internal carotid arteries during endarterectomy; and

FIG. 6 depicts an indwelling common lumen shunt and filter deployedwithin an artery during an endarterectomy procedure.

DETAILED DESCRIPTION OF THE INVENTION

The devices and methods disclosed herein function to prevent embolicmaterial from migrating downstream (into the brain, organs, extremitiesof the limbs, etc.) during vascular surgery. The devices and methodsherein are useful during any procedure where vessels are cut open forthe purpose of removing occlusions or performing other types of repairthat may require the use of shunting to maintain distal blood flow.

According to one embodiment, the shunt is as depicted in FIG. 1. Theshunt includes elongated tubular member 10 having lumen 11 which extendsfrom proximal opening 12 to distal opening 13. Within an intermediatesection of tubular member 10, the shunt includes a "Y" arm, or secondtubular member 14 having lumen 15 which branches away from main lumen11. Thus, at one end, lumen 15 merges and communicates with lumen 11,while at the other end, lumen 15 terminates at hemostatic valve 16 whichpermits device introduction. The direction of blood flow through theshunt during use is depicted by arrow 17. The "communicating lumen"shunt as depicted in FIG. 1 will typically be constructed from a verysoft, atraumatic material, e.g., silicon, latex, urethane. The length oftubular member 10 from its proximal opening to its distal opening willtypically be greater than 5 cm, more typically greater than 8 cm, moretypically greater than 10 cm, more typically greater than 12 cm, moretypically 15 cm or more in length. Meanwhile, the outer diameter oftubular member 10 will generally be 3 mm or greater, more generally 4 mmor greater, more generally 5 mm or greater. The foregoing ranges are setforth solely for the purpose of illustrating typical device dimensions.The actual dimensions of a device constructed according to theprinciples of the present disclosure may obviously vary outside of thelisted ranges without departing from those basic principles disclosedherein.

In a second embodiment, the shunt includes elongated tubular member 10with lumen 11 as depicted in FIG. 2. A second tubular member 14 isprovided having lumen 15 extending from hemostatic valve 16 at aproximal end to opening 18 at a distal end thereof. Lumen 15 thereforeincludes a first segment which runs substantially parallel to lumen 11of main tubular member 10, and a second segment which branches away fromlumen 11 and terminates proximally at hemostatic valve 16. This"non-communicating lumen" shunt allows blood to flow in the direction ofarrow 17 when the shunt is in use, and this shunt is constructed fromthe materials and according to the device parameters given above.

In use, it will be understood that secondary lumen 15 defines apassageway for introduction of a medical instrument, e.g., a bloodfilter device, within an artery during an arteriotomy or endarterectomyprocedure. With reference to FIG. 3, the use of a shunt as disclosedherein will be described in the context of an endarterectomy procedure.A typical site of atherosclerotic plaque build-up is in the commoncarotid artery near the segment which branches to the internal carotidartery and external carotid artery. Segment 62 of artery 61 havingplaque build-up is located and exposed through an incision made in theneck of a patient. Tourniquet 31 (Rummel tourniquet) is placed looselyaround the common carotid artery. A Bulldog clamp (not shown) is thensecured on the internal carotid artery. Next, a DeBakey clamp (notshown) is placed on the common carotid artery proximal (upstream) of thetourniquet. The external carotid artery (not shown) is secured with aBulldog clamp. This order of vessel clamping is significant because theclamp on the internal carotid artery is effective to catch any embolicdebris dislodged by the DeBakey clamp placed on the common carotidartery.

With the clamps in place, the surgeon makes a longitudinal incision inthe artery using scissors to expose the region of the artery containingplaque material. A shunt as depicted in FIG. 1 or FIG. 2 is gripped withforceps in the distal region. A second forceps is secured to theproximal region of the shunt to prevent blood escape. The Bulldog clampwhich secures the internal carotid artery is loosened to allowback-bleeding while the distal opening 13 of shunt 10 is advanceddistally into the internal carotid artery. When the shunt has beensuccessfully placed in the internal carotid artery, it is secured byJavid clamp 32 to prevent further back-bleeding. It should be noted thatduring advancement of the distal opening of the shunt into the internalcarotid artery, care must be taken to avoid scraping and therebydislodging debris from the walls of the vessel. For this reason, theclamp on the internal carotid artery is loosened and allowed toback-bleed during the process so that antegrade blood flow blows thevessel walls apart so that tubular member 10 can be advanced through thecenter.

The second forceps secured to the proximal region of the shunt isreleased in order to vent air from the interior lumen of the shunt. Ablood filter device is deployed through the hemostatic valve andadvanced through lumen 15 into common lumen 11 and through distalopening 13 into artery 61. The blood filter device will typicallyinclude an elongated member 41 (guidewire, sheath, etc.) having aproximal end with control mechanism 43 for activating the filter, andfiltration mesh 42 suspended on an expansion frame disposed about thedistal end of elongated member 41. The construction and use of expansionframe, associated filter mesh 42, and control mechanism 43 have beenthoroughly discussed in earlier applications including Barbut et al.,U.S. application Ser. No. 08/553,137, filed Nov. 7, 1995, now abandonedBarbut et al., U.S. application Ser. No. 08/580,223, filed Dec. 28,1995, now abandoned Barbut et al., U.S. application Ser. No. 08/584,759,filed Jan. 9, 1996, now abandoned Barbut et al., U.S. application Ser.No. 08/640,015, filed Apr. 30, 1996, now U.S. Pat. No. 5,769,816, Barbutet al., U.S. application Ser. No. 08/645,762, filed May 14, 1996, andBarbut et al., U.S. application Ser. No. 08/683,503, filed Jul. 17,1996, now U.S. Pat. No. 5,662,671 and the contents of each of theseprior applications are incorporated herein by reference in theirentirety. It will be understood that the design and use of a filtermesh, associated expansion frame, and control mechanism as discussed inthese applications is fully applicable to the use of such filter andexpansion frame on a guidewire or arterial catheter system as disclosedherein.

The filter is maintained in a contracted state during entry throughlumen 15, and lumen 11. Once the filter has been advanced beyond distalopening 13 of shunt 10, filter 42 is expanded to an enlarged diameterwhich covers a substantial portion of the cross-sectional area of vessel61. Filter 42 is maintained in place during the remaining surgery inorder to capture embolic material dislodged during the procedure.

Next, the proximal opening of the shunt is advanced proximally into thecommon carotid artery until it abuts against the DeBakey clamp.Tourniquet 31 is tightened and the DeBakey clamp released to allow thesurgeon to slide the shunt further proximal. Once the shunt and filterare in place and operational as depicted in FIG. 3, it is generallydesirable to evaluate shunt function using a Doppler probe. An audibleflow signal will typically confirm patency. FIG. 3A shows across-sectional view of shunt 10 and elongate member 41 within vesselsegment 62, taken through section line 3A--3A. The endarterectomyprocedure is then performed within the dissected region of the artery.The plaque or atheroma material typically has the consistency of a thickshell. This material is dissected and peeled out of the vessel,preferably in one or a small number of large pieces. Such a monolithicremoval is preferred to breaking of the plaque into small pieces as thelatter may be lost in the circulation and result in emboli.

The dissected vessel is then closed by suturing both ends of the slittoward the center until a small hole remains in the common carotidartery, as described in Loftus, Carotid Endarterectomy Principles andTechniques; Quality Medical Publishing, Inc.: St. Louis, Mo., 1995. Theshunt is then gripped by two clamps spaced by a short distance. Filtermesh 42 is contracted to a small diameter, holding captured embolicmaterial trapped within the mesh. The filter is then withdrawn fromvessel 61 into lumen 11, and then into lumen 15 and removed fromhemostatic valve 16. The shunt is cut by scissors between the clamps.Both resulting pieces of the shunt are removed from the common carotidartery.

The clamp on the internal carotid artery is briefly loosened and allowedto back-bleed in order to purge air from the dissected region 62 ofvessel 61. The clamp on the external carotid artery is similarlyloosened briefly to back-bleed and purge air from the affected segmentof the external carotid artery. The surgeon checks for thrombi enclosedwithin the affected segment 62 of vessel 61, and for inadvertent closurefrom the suture line having caught an unintended portion of the back ofthe vessel. Heparinized saline is injected into the small opening whichremains. The last suture is tied to completely close the incision in thedissected region of vessel 61. The clamp on the external carotid arteryis removed, and the clamp on the common carotid artery is removed. Aftera delay of 10 seconds, the clamp on the internal carotid artery isremoved. This sequence ensures that any inadvertent debris or air isflushed to the external carotid artery rather than the internal carotidartery and the patient thereby avoids neurologic harm.

In another embodiment, the shunt is secured to the vessel walls usingone or more balloon occluders as depicted in FIG. 6. The use of balloonocclusion eliminates the need to apply compressive clamps (numerals 31and 32 in FIG. 3) to secure the shunt within the vessel, and therebyreduces the risk of debris dislodgement during shunt installation. Withreference to FIG. 6, shunt 10 includes one or more balloon occluder 35at its proximal and/or distal ends, the balloon occluder being disposedcircumferentially around the tubing of the shunt. Occluder 35 is influid communication with inflation lumen 37, inflation port 38, andoptionally tubing 39 for saline injection. Thus, in use, the proximal ordistal end of the shunt is positioned as described above, while occluder35 is in a deflated state. Saline, or other biotolerable fluid, isinjected through port 38 until occluder 35 enlarges into contact withthe inner diameter of vessel 61, thereby sealing the vessel from bloodflow. A cuff or C-clamp 36 may be fitted about the vessel to preventhyperexpansion, minimize internal slippage of the balloon occluder, andprovide a tight seal within the vessel. After the endarterectomyprocedure, saline is withdrawn to deflate occluder 35 before the shuntis removed from the vessel.

In another embodiment, the shunt and filtration assembly are separatedfrom another as depicted in FIG. 4. Deployment of the filtrationassembly makes use of introducer sheath 51 having hemostatic valve 52 atone end thereof. Introducer sheath 51 is inserted through an incision inthe wall of artery 61 downstream or distal to the site of arteriotomy62. Introducer 51 is shaped to receive catheter sheath 43 which receiveselongate member 44 having filter mesh 42 operably disposed at a distalregion thereof. Expansion and contraction of filter 42 is controlled bymechanism 45 which operates at the proximal region of elongate member44. Thus, in use, after the artery is selected and isolated, introducer51 is inserted through an incision created in the wall of artery 61.Filter catheter 43 is inserted through hemostatic valve 52 and into thelumen of vessel 61 with filtration assembly 42 being in a contractedcondition. Once in place, control mechanism 45 is operated to expandfilter 42 so that it covers most, if not all, of the cross-sectionalarea of vessel 61. With the filter in place, an endarterectomyprocedure, which includes steps of clamping (using Bulldog clamp 32 andoptionally vascular occlusion clamp 33), installation of a normal shunt,arteriotomy, shunt removal, and unclamping, is conducted in accordancewith the description given above. Thereafter, filter 42 is contractedand removed from artery 61 through introducer 51. In a final step,introducer 51 is removed from the artery and the opening in artery 61 issutured.

It will be understood that the ordering of steps can be modified so thatintroduction of filter 42 may occur at any point in the procedure.However, in a preferred embodiment, the filter is deployed beforearteriotomy begins and the filter is removed after arteriotomy has beencompleted. In this manner, filter 42 is available to capture all embolicmaterial which results from the manipulative steps of the arteriotomyprocedure, e.g., clamping, unclamping, installation of tourniquet,installation and movement of shunt 10, cutting of vessel 61, suturingthe vessel, and shunt removal. Thus, the method depicted in FIG. 4constitutes a preferred embodiment insofar as it allows the surgeon tomaintain filter 42 deployed within the vessel throughout the arteriotomyprocedure.

In another embodiment, a non-indwelling shunt is used to bypass anendarterectomy region as depicted in FIG. 5. This figure shows commoncarotid artery 65 which branches into external carotid artery 66 andinternal carotid artery 67, and which includes an affected region 62having atherosclerotic plaque 63 disposed on the lumen thereof. Distalopening 13 of shunt 10 is inserted into vessel 61 through an incision.Back-bleeding through the shunt occurs from the distal opening 13 oflumen 11 in order to purge air from within the shunt. After the shunt ispurged, proximal opening 12 is secured by a clamp (not shown). Filtercatheter 43 having elongate member 44, filter mesh 42, and controlmechanism 45 disposed thereon, is inserted into the lumen of shunt 10through hemostatic valve 16 and thereafter advanced into the internalcarotid artery 67 with filter 42 in a collapsed state. Using controlmechanism 45, filter 42 is enlarged to cover substantially all of thecross-sectional area of the internal carotid artery lumen. Proximalopening 12 of shunt 10 is then inserted into common carotid artery 65through an incision.

With the filter in place, an endarterectomy procedure is conducted onaffected region 62 in order to remove deposits 63 as depicted in FIG. 5.This region of the carotid artery is isolated using clamps 31, 33, and34 as described above, and incision 64 is created to expose plaquedeposits 63 within region 62. The plaque is removed, the area iscleaned, the incision is closed, and the clamps are removed in order topurge any remaining gas. The final sutures are then installed tocomplete the closure of incision 64, and blood flow is reestablishedwhile filter mesh 42 remains in place. This sequence ensures that anyremaining debris is captured by filter 42 and is not allowed to enterthe brain as emboli. Filter 42 is then collapsed and removed from theinternal carotid artery 67 into shunt 10, and thereafter throughhemostatic valve 16. Finally, the distal end of the shunt is removedfrom the internal carotid artery, the incision is sutured, the proximalend of the shunt is removed from the common carotid artery, and theincision in the common carotid artery is sutured. In this manner, thepatient is protected from embolization to the brain throughout thearteriotomy procedure.

Referring again to FIG. 4, the introducer sheath 51 will typically havean external diameter of 5-12 French, more preferably 6-8 French. Withreference to the filter device, the diameter at the distal end willtypically be 1-3 mm, more preferably 1.5-2.5 mm. The filter is generallyactivated from the proximal end and is deployed from within a smallsheath or on the outside of a guidewire or small tube. The length of thefilter device is generally 20-40 cm and the deployed diameter of filtermesh 42 will typically be 2 mm or larger, more preferably 4 mm orlarger, more preferably 6 mm or larger, more preferably 8 mm or larger,more preferably 10 mm or larger, and generally will be 2-10 mm. Theforegoing ranges are set forth solely for the purpose of illustratingtypical device dimensions. The actual dimensions of a device constructedaccording to the principles of the present disclosure may obviously varyoutside of the listed ranges without departing from the basic principlesdisclosed herein.

It will be understood that filtration is an important aspect of theendarterectomy shunt and methods disclosed herein. To filter bloodeffectively, i.e., to capture embolic material, without undulydisrupting blood flow, the mesh must have the appropriate physicalcharacteristics, including area (A_(M)), thread diameter (D_(T)), andpore size (S_(P)). In the carotid arteries, the mesh 42 must permit flowrates as high as 0.15 L/minute or more, more preferably 0.2 L/minute ormore, more preferably 0.25 L/minute or more, more preferably 0.3L/minute or more, more preferably 0.35 L/minute or more, more preferably0.4 L/minute or more, more preferably 0.45 L/minute or more, and mostpreferably 0.5 L/minute or more at pre-filter maximum systolic pressures(proximal to the mesh) of around 200 mm Hg or less.

In order to capture as much of the dislodged material as possible, meshwith the appropriate pore size must be chosen. With reference to embolicmaterial dislodged from the aorta, individual particle diameter rangesfrom 0.05 mm to 2.88 mm, with a mean diameter of 0.85 mm, and individualparticle volume ranges from 6.5×10⁻⁵ mm³ to 12.45 mm³, with a meanparticle volume of 0.32 mm³. Approximately 27 percent of the particleshave been found to measure 0.6 mm or less in diameter. During cardiacbypass surgery in particular, the total aortic embolic load has beenfound to range from 570 mm³ to 11200 mm³, with a mean of 3700 mm³, andan estimated cerebral embolic load has been found to range from 60 mm³to 510 mm³, with a mean of 276 mm³. During carotid endarterectomy,materials dislodged as emboli have similar characteristics to those ofaortic materials.

It should also be understood that the embolic material against which thepresent devices and method protect may include gaseous bubblesinadvertently introduced during the surgical procedure. Air emboli are acommon and dangerous occurrence during all types of surgeries. They arepotentially most dangerous if allowed to enter the cerebral circulationand cause ischemic events, which may lead to stroke. The type of surgerywhere this is most likely to occur is surgery on the heart and ascendingaorta, but may also occur during endarterectomy. Currently, surgeonsmake great efforts to de-air and vent the heart and vasculature after aprocedure to eliminate air prior to closing the incision and/or taking apatient off of cardiopulmonary bypass. Nevertheless, a small amount ofair always remains and is potentially dangerous.

Thus, the filter assembly disclosed herein acts to retain large airbubbles, and under sufficient pressure, causes them to be broken intomuch smaller bubbles which are much less potentially harmful. A typicalpore size for the aortic filter is about 100 μm. When a bubble greaterthan 100 μm diameter encounters the filter, there must be sufficientpressure on the proximal side of the filter to force the bubble throughthe pore. The surface tension of the blood generally prevents the bubblefrom deforming and extruding through the pore, but rather the bubblebreaks apart into a plurality of bubbles small enough to pass freelythrough the pore. The filter thereby acts as a bubble sieve.

The benefit of reducing the size of the interactive bubbles is twofold.First, the potential of a bubble to cause ischemia is directly relatedto its diameter. The larger the bubble, the more likely it is to blockblood flow to a larger area of the brain. Smaller bubbles may blocksmaller arteries, but will have less overall ischemic effect. Second,smaller bubbles will be absorbed into tissue and cells more quickly thanlarge bubbles, because of their greater surface area to volume ratio.The net effect is smaller bubbles which may make their way into thebrain, and bubbles which will be more quickly metabolized furtherreducing risk of embolic ischemia.

Another method by which large bubbles can be rendered into smallerbubbles is due to velocity and momentum effects. During moments of peaksystolic cardiac output, the blood velocity from the heart is at itsmaximum (100-150 cm/s). If a bubble is trapped against the intraaorticfilter and is subject to instantaneous high velocity blood flow, themomentum of the blood on the bubble will cause the bubble to shatterinto smaller bubbles. The smaller bubbles will then "escape" through thepores in the filter if they have been rendered small enough.

The area of the mesh required for the device herein, having all of thedesirable properties disclosed herein, for use in the carotid arteriesis calculated from Bernoulli's equation as described in Barbut et al.,U.S. Application Serial No., U.S. application Ser. No. 08/553,137, filedNov. 7, 1995, now abandoned Barbut et al., U.S. application Ser. No.08/580,223, filed Dec. 28, 1995, now abandoned Barbut et al., U.S.application Ser. No. 08/584,759, filed Jan. 9, 1996, now abandonedBarbut et al., U.S. application Ser. No. 08/640,015, filed Apr. 30,1996, now U.S. Pat. No. 5,769,816 and Barbut et al., and U.S.application Ser. No. 08/645,762, filed May 14, 1996. Thus, in oneembodiment, a filter for use in the carotid arteries is provided with amesh having dimensions within the following ranges: mesh area is 10-200mm², more preferably 20-150 mm², more preferably 35-100 mm², morepreferably 50-75 mm² ; mesh thickness is 60-280 μm, more preferably70-270 μm, more preferably 80-260 μm, more preferably 90-250 μm, morepreferably 100-250 μm, more preferably 120-230 μm, more preferably140-210 μm; thread diameter is 30-145 μm, more preferably 40-135 μm,more preferably 50-125 μm, more preferably 60-115 μm, more preferably70-105 μm; and pore size is 500 μm or less, more preferably 50-180 μm,more preferably 50-170 μm, more preferably 50-160 μm, more preferably60-150 μm, more preferably 60-140 μm, more preferably 60-130 μm, morepreferably 60-120 μm, more preferably 60-110 μm, more preferably 60-100μm, more preferably 60-90 μm, more preferably 60-80 μm, and usuallylarger than at least a red blood cell. In a preferred embodiment of theinvention, mesh area is 50-75 mm², mesh thickness is 100-150 μm, threaddiameter is 30-100 μm, and pore size is 50-150 μm.

Once appropriate physical characteristics are determined, suitable meshcan be found among standard meshes known in the art. For example,polyester meshes may be used, such as meshes made by Saati Corporationand Tetko Inc. These are available in sheet form and can be easily cutand formed into a desired shape. In a preferred embodiment, the mesh issonic welded into a cone shape. Other meshes known in the art, whichhave the desired physical characteristics, are also suitable.Anticoagulants, such as heparin and heparinoids, may be applied to themesh to reduce the chances of blood clotting on the mesh. Anticoagulantsother than heparinoids may also be used, e.g., monoclonal antibodiessuch as ReoPro (Centocor). The anticoagulant may be painted or sprayedonto the mesh. A chemical dip comprising the anticoagulant also may beused. Other methods known in the art for applying chemicals to mesh maybe used.

In an embodiment of the devices suited for placement in the carotidarteries, the expansion frame comprises an inflation seal with inflationsystem as discussed in U.S. application Ser. Nos. 08/580,223,08/584,759, 08/640,015, 08/645,762, and 08/683,503. The expansion means,when fully inflated, has a thickness of 0.5-1 mm. The dimensions of theexpansion means may be adjusted in alternative embodiments adapted foruse in vessels other than the carotid arteries. Alternatively, anexpandable frame other than a balloon inflation seal may be used withthe devices and methods disclosed herein. Expandable frames includeumbrella frames with a plurality of arms as described in U.S.application Ser. Nos. 08/533,137, 08/580,223, and 08/584,759.

All components of this device should be composed of materials suitablefor insertion into the body. Additionally, sizes of all components aredetermined by dimensional parameters of the vessels in which the devicesare intended to be used. These parameters are known by those skilled inthe art.

Filtration of blood in the carotid arteries will usually be conductedwhile the heart is functioning normally, i.e., without the use ofcardiopulmonary bypass. Thus, blood pressure will be typically 50-200 mmHg, blood flow will be approximately between 0.15-0.5 L/minute, and thepressure gradient will have no more than a 40 mm Hg drop across thefilter when open (i.e., the filter may not be used in some embodiments).Modification of the operational characteristics set forth above for usein vessels other than the carotid arteries are readily ascertainable bythose skilled in the art in view of the present disclosure. An advantageof all embodiments including a filter disclosed herein is that both theshunt and filter enter the vessel through a single incision created forthe shunt, and therefore the devices and methods herein economize onincisions made in the arteries.

It will also be understood that the filter device may be deployed byinsertion through the "Y" arm on the shunt during or after installationin an artery, and for each disclosed method, the shunt and "Y" armlumens may be common (merging) or separate lumens as depicted in FIG. 1and FIG. 2, respectively. Moreover, insertion may be made next to theshunt, before, during, or after the shunt is installed. Insertion of thefilter device may occur distal to the arteriotomy site, the shunt, andthe occlusion clamp through an introducer, either intraoperatively orpercutaneously. Where insertion of the filter device occurspercutaneously, distal to the region, the filter device may be insertedand deployed prior to interventional therapy such as arteriotomy,angioplasty, or stent deployment.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced which will still fall within the scope of the appendedclaims. In particular, it should be understood that, although certainfeatures (such as balloon occlusion) are shown by reference to only asingle embodiment, those features are applicable to all otherembodiments disclosed herein.

What is claimed is:
 1. A shunt for maintaining distal blood flow duringan arteriotomy procedure, comprising:a first tubular member having aproximal end, a distal end, and a lumen therebetween, the proximal endhaving an opening in communication with the lumen, the proximal openingis adapted to receive blood from a first region of an artery, the distalend having an opening in communication with the lumen, the distalopening is adapted to release blood into a second region of the artery;a second tubular member having a proximal end, a distal end, and a lumentherebetween which merges at an angle of substantially less than 90° andcommunicates at its distal end with the lumen of the first tubularmember, thereby allowing introduction of a medical device into the lumenof the first tubular member; a hemostatic valve attached to the proximalend of the second tubular member, the valve acting to prevent loss ofblood from the lumen of the second tubular member and to permit theintroduction of the medical device into the lumens of the second andfirst tubular members; and a blood filter disposed on an elongatedinstrument and inserted through the hemostatic valve into the lumen ofthe second tubular member.
 2. A method for maintaining distal blood flowduring an arteriotomy procedure, comprising the steps of:providing ashunt comprising a tubular member having a proximal opening, a distalopening, a first lumen therebetween and a second lumen having a firstopening which merges and communicates with the first lumen of thetubular member and a second opening adapted to receive a blood filterdevice; inserting the distal opening of the shunt into a first region ofa carotid artery and securing the shunt against the lumen of the carotidartery; inserting the blood filter into the second opening of the secondlumen; advancing the blood filter into and beyond the lumen of thetubular member; expanding the blood filter to cover a substantialportion of the cross-sectional area of the carotid artery; inserting theproximal opening into a second region of the carotid artery and securingthe shunt against the lumen of the carotid artery; and performingendarterectomy on a region of the carotid artery which lies between theproximal opening and the distal opening of the shunt.
 3. The method ofclaim 2, wherein the blood filter device is deployed after the distalopening and proximal opening are inserted and secured to the carotidartery.
 4. The method of claim 2, wherein the blood filter device isinserted into the carotid artery downstream of a bifurcation.
 5. Themethod of claim 2, wherein the blood filter device is deployed beforethe distal opening and proximal opening are inserted and secured to theartery.
 6. The method of claim 2, wherein the proximal opening isinserted and secured to the second region of the artery before thedistal opening is inserted and secured to the first region of theartery.
 7. The method of claim 2, wherein the step of expanding theblood filter device comprises the step of expanding an inflation seal towhich the blood filter is attached.
 8. The method of claim 2, whereinthe step of securing the shunt against the lumen of the carotid arteryincludes securing the shunt using a clamp.
 9. The method of claim 2,wherein the step of securing the shunt against the lumen of the carotidartery includes securing the shunt using a balloon occluder.
 10. Amethod for maintaining distal blood flow during an arteriotomyprocedure, comprising the steps of:providing a shunt comprising atubular member having a proximal opening, a distal opening, a firstlumen therebetween, and a second lumen having a first segment which liessubstantially parallel to the first lumen of the tubular member and asecond segment which branches away from the first lumen of the tubularmember; inserting the distal opening of the shunt into a first region ofa carotid artery and securing the shunt against the lumen of the carotidartery; inserting the blood filter into the second segment of the secondlumen; advancing the blood filter into and beyond the first segment ofthe second lumen; expanding the blood filter to cover a substantialportion of the cross-sectional area of the carotid artery; inserting theproximal opening into a second region of the carotid artery and securingthe shunt against the lumen of the carotid artery; and performingendarterectomy on a region of the carotid artery which lies between theproximal opening and the distal opening of the shunt.
 11. The method ofclaim 10, wherein the step of expanding the blood filter comprises thestep of expanding an inflation seal to which the blood filter isattached.
 12. The method of claim 10, wherein the blood filter device isinserted into the carotid artery downstream of a bifurcation.
 13. Themethod of claim 10, wherein the blood filter device is deployed afterthe distal opening and proximal opening are inserted and secured to thecarotid artery.
 14. The method of claim 10, wherein the blood filter isdeployed before the distal opening and proximal opening are inserted andsecured to the artery.
 15. The method of claim 10, wherein the proximalopening is inserted and secured to the second region of the arterybefore the distal opening is inserted and secured to the first region ofthe artery.
 16. The method of claim 10, wherein the step of securing theshunt against the lumen of the carotid artery includes securing theshunt using a clamp.
 17. The method of claim 10, wherein the step ofsecuring the shunt against the lumen of the carotid artery includessecuring the shunt using a balloon occluder.